Field‐aligned neutral wind bias correction scheme for global ionospheric modeling at midlatitudes by assimilating FORMOSAT‐3/COSMIC h_mF₂ data under geomagnetically quiet conditions

Abstract

This study demonstrates the usage of a data assimilation procedure, which ingests the FORMOSAT-3/COSMIC (F3/C) h m F 2 observations to correct the model wind biases to enhance the capability of the new global Ionosphere Plasmasphere Electrodynamics (IPE) model under geomagnetically quiet conditions. The IPE model is built upon the field line interhemispheric plasma model with a realistic geomagnetic field model and empirical model drivers. The h m F 2 observed by the F3/C radio occultation technique is utilized to adjust global thermospheric field-aligned neutral winds (i.e., a component of the thermospheric neutral wind parallel to the magnetic field) at midlatitudes according to a linear relationship between time differentials of the field-aligned wind and h m F 2 . The adjusted winds are further applied to drive the IPE model. The comparison of the modeled electron density with the observations of F3/C and ground-based GPS receivers at the 2012 March equinox suggests that the modeled electron density can be significantly improved in the midlatitude regions of the Southern Hemisphere, if the wind correction scheme is applied. Moreover, the F3/C observation, the IPE model, and the wind bias correction scheme are applied to study the 2012 Southern Hemisphere Midlatitude Summer Nighttime Anomaly (southern MSNA)/Weddell Sea Anomaly (WSA) event at December solstice for examining the role of the neutral winds in controlling the longitudinal variation of the southern MSNA/WSA behavior. With the help of the wind bias correction scheme, the IPE model better tracks the F3/C-observed eastward movement of the southern MSNA/WSA feature. The apparent eastward movement of the southern MSNA/WSA features in the local time coordinate is primarily caused by the longitudinal variation in the declination angle of the geomagnetic field that controls the field-aligned projection of both geographic meridional and zonal components of the neutral wind. Both the IPE simulations and the F3/C observations show the significant longitudinal variation in the speed of the eastward movement of the southern MSNA/WSA.

PCA and vTEC climatology at midnight over mid-latitude regions

“…Therefore, we support the belief that the thermospheric wind is one of the most important components of the MSNA Thampi et al 2009). The winter anomaly in the F2 region is defined as the condition in which a greater daytime electron density is seen at the F2 peak in winter than in summer (Burns et al 2014;Rishbeth and Garriot 1969). This anomaly is primarily due to greater winter to summer differences of [O]/[N2] at solar maximum than at solar minimum for daytime hours.…”

“…This effect varies on different timescales, but the rate of change of electron density also depends on loss processes, by recombination, and by electron movement (in terms of mean drift velocity), all of which are related by the continuity equation. According to the Chapman photochemical theory (Rishbeth and Garriot 1969), ionospheric electron content should have a diurnal variation with maximum values at noontime, when the solar zenith angle is lowest. Ionospheric electron density at any time and location depends on many factors: the composition of the neutral atmosphere and its physical conditions, such as density and temperature, the solar spectrum and any energetic particle fluxes able to ionize the atmospheric plasma, and finally the loss processes, both chemical and by transport.…”

The fast development of solar terrestrial sciences in Taiwan

“…From the first three-dimensional structure of ionospheric WSA, it can be realized that WSA is simpler part of a bigger ionospheric anomaly, namely, the middle latitude summer nighttime anomaly (MSNA) Chen et al 2011Chen et al , 2013. Meanwhile, the MSNA/WSA eastward movement signature have also been comprehensively studied using F3/C observations Liu et al 2015;Chang et al 2015b) and model simulations Sun et al 2015). Also, a new type of low latitude plasma structure located underneath the EIA peaks is discovered, and their corresponding physical mechanism is proposed for the first time (Lee et al 2012b;Chen et al 2014c).…”

“…Liu et al (2016) surveyed the worst-case GPS scintillations on the ground estimated from radio occultation observations of F3/C during 2007-2014 and are ready to develop an empirical model for the ionospheric S4 scintillation. Currently, the nowcast and forecast data assimilation models with the neutral atmosphere have been developed (Lee et al 2012c;Hsu et al 2014;Sun et al 2015).…”

Data Assimilation of Ground‐Based GPS and Radio Occultation Total Electron Content for Global Ionospheric Specification

“…The Global Assimilative Ionospheric Model and the Global Assimilation of Ionospheric Measurements developed by the University of Southern California/Jet Propulsion Laboratory (Hajj et al, ; Komjathy et al, ; Wang et al, ) and the Utah State University (Scherliess et al, ; Schunk et al, ) have a capability of assimilating multiple sources of ionospheric observations into the time‐dependent and physics‐based ionospheric models. Recently, the importance of treating the ionosphere‐thermosphere as a coupled system in the ionospheric data assimilation has been studied (e.g., Chen et al, ; Hsu et al, ; Lee et al, , ; Matsuo & Araujo‐Pradere, ; Sun et al, ).…”